(Cover) - EN Showbiz - Sienna Miller says her "brain doesn't work" since she gave birth.

The actress and her fianc Tom Sturridge welcomed their daughter Marlowe Ottoline Layng Sturridge into the world at the beginning of July.

Sienna loves motherhood but she is still getting used to constantly caring for someone else.

"I'm doing good though my brain doesn't work," Sienna told Parade.com. "Marlowe is sleeping upstairs [at the moment]."

The actress appears in HBO film The Girls which is out later this year. Sienna plays Tippi Hedren in the movie, which chronicles Alfred Hitchcock's obsession with Tippi after he directed her in movies The Birds and Marnie. Sienna called her work on the film "intense", "challenging" and "a lot of fun".

"It's always difficult when you're trying to imitate someone as effortlessly glamorous as Tippi..." Sienna said. "I tried to capture the essence but it wasn't supposed to be an exact replica. It was really challenging and a lot of fun."

Sienna also discussed the pressure of playing a character based on a real person. Having Tippi on hand to offer her advice was a great relief when she was filming.

"I've played real people before and it's always a huge responsibility to do it justice. I was very fortunate to have Tippi over the phone and over email," Sienna explained. "She is an amazing character to take on and she is very gracious in imparting information to me." (C) Cover Media